Technical Abstract:
The shift in equilibrium towards excess reactive oxygen or nitrogen species production from innate antioxidant defense in brain is a critical factor in the declining neural functions and cognitive deficits accompanying age. In aging, there are noticeable alterations in the membrane microenvironment, with increased oxidized proteins and lipids, altered calcium buffering, accumulation of damaged organelles and protein structures, weak neurotransmitter release, and dystrophy and death of neurons. Previous studies from our laboratory have reported that walnuts, rich in polyphenols, antioxidants, and omega fatty acids such as alpha linoleic acid (ALA) and linolenic (LA), improve the age-associated declines in cognitive and neural deficits in rats. Possible mechanisms of action of these effects include enhancing protective signaling, altering membrane microstructures, decreasing inflammation, and preventing accumulation of polyubiquitinated protein aggregates in critical regions of the brain. In the current study, we investigated whether the serum collected from aged animals fed with walnut diets (0, 6% and 9%) would enhance protection on stressed BV2 microglial and HT22 hippocampal neurons, in vitro. In the growth medium, fetal bovine serum (FBS) was substituted with the serum collected from 22 month old rats fed with either walnut or control diets for 12 weeks. Walnut diet serum (6 and 9%) significantly attenuated dopamine-(DA-)induced neurotoxicity, as measured by recovery from calcium influx in potassium chloride-(KCl-)induced depolarized hippocampal neurons. Additionally, walnut diet serum (6 and 9%) significantly attenuated lipopolysaccharide-(LPS-)induced nitrite release in the microglial cells. Neither control serum nor FBS alone (negative control) elicited similar rescuing effects on either type of brain cell. While identification of the individual metabolites, as well as the measurement of oxidant/antioxidant enzymes in these sera are being done, preliminary results strongly suggest protection or enhancement of membrane-associated functions in brain cells by walnut serum metabolites.